In general, it is used in the dialysis treatment a blood circuit for extracorporeally circulating collected blood of a patient and returning it again to a body of a patient. The blood circuit mainly comprises an arterial blood circuit and a venous blood circuit to be connected to a dialyzer (blood purification means) provided with a hollow fiber membrane. Puncture needles are adapted to be mounted on tip ends of the arterial blood circuit and the venous blood circuit to perform the extracorporeally blood circulation in the dialysis treatment with the puncture needles being punctured to a patient.
After completion of the dialysis treatment, a blood-returning operation for returning blood remained in the blood circuit, dialyzer, arterial air-trap chamber, venous air-trap chamber etc to a patient is required. In such a blood-returning operation of the prior art, the blood in the blood circuit has been substituted with physiological saline (substitution solution) by introducing the physiological saline in the middle of the arterial blood circuit as disclosed e.g. in Patent Document 1 below.
It is performed in the prior art to make automation of the blood-return operation easy as disclosed in Patent Document 2 to return blood in the blood circuit and dialyzer to a body of patient through the arterial puncture needle and the venous puncture needle by rotating a blood pump reversely to the rotation in the dialysis treatment with inversely filtrating the dialysate (substituting solution) from a dialysate flow path to a blood flow path and by substituting the blood remained in the blood circuit with the inversely filtrated dialysate.